Sealing leaking rivets

Rbailey19

Recruit
Joined
May 26, 2020
Messages
1
I recently picked up an old 14’ aluminum boat dirt cheap and it’s got some black tar looking stuff on the bottom covering the rivets. It’s rock hard, doesn’t scrape off and not one of those spots leak. Just curious what that might be so I can do the rest of the rivets with it. Thanks.
 
Top